Means for reducing interference



Dec. 29 1925.

O. E, BUCKLEY MEANS FOR REDUCING INTERFERENCE Filed May 2, 1921 Patented Dec. 29, 19 25.

UNITED STATES 1,567,316 PATENT OFFICE.

OLIVER E. BUCKLEY, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MEANS FOR REDUCING INTERFERENCE.

Application filed May 2 To all w]: am it 112,04 concern 7 Be it known that I, OLIVER E. BUCKLEY, a citizen of the United States of America, residing at Maplewood, in the county of Essex, State of New Jersey,l;have invented certain new 'and usefu'l Improvements in --l\{eans for Reducing Interference, of which concise, and

' accurate balance in cases in which cables are operated by the duplex method.

The object of this invention is attained by balancing against the main cable conductor a similar conductor of short length laid parallel to the main conductor and terminated in an artificial line having practically the same electrical characteristics as the cable and by paralleling both the main cable conductor and the balancing or sea ground conductor with secondary artificial lines having practically equal electrical characteristics. By means of these-secondary artificial lines provision is made to establish a complete and accurate balance for duplex operation.

The limiting speed of signaling over long submarine telegraph cables is in most cases determined by interference arising either from lack of perfect duplex balance or from external sources. lack of perfect duplex balance could, of course, be reduced by more carefully matching the artificial line to the cable, but in the systems at present commonly used an accurate balance, even if obtained at one time, cannot be maintained for longsince temperature changes may affect the electrical constants of the cable rendering the balance imperfect.

The interference from external sources may arise either from neighboring power circuits or may come from natural sources. One method which has been employed to reduce the external interference is to make the ground connection of the balancing artificial line to a second conductor called the sea ground conductor which runs arallel to the main cable conductor usual y in the same sheath to a point several miles from for correcting the balance it at any time it 119 That which arises from 1921. serial 110. 468,129.'

shore where a ground connection is made to the cable sheath. This sea ground conductor generally has the same electricalconstants as the main cable conduct-on. Although some advantage is obtained by this procedure, disturbances are not completely eliminatedfor although the same electromotive forces are induced both in the main conductor and in the sea ground conductor, the currents produced in the two conductors are different owing to the difference in impedance to ground. In order to completely eliminate the effect of external interference by means of a sea ground, it would be necessary to run the sea ground conductor out to a point sufliciently far from the receiving station that no sensible disturbance is received from beyond that point, and there to terminate it in an artificial line having substantiallythe same impedance as the cable beyond that point. If the main cable conductor is now balanced by such a sea ground conductor and artificial line, the two terminals of the receiving apparatus will be subject to equal variations of potential as a result of currents induced in the cable conductor and sea ground conductor from external sources and such disturbances will have no effect on a receiving instrument. A further, advantage is obtained in that the cable conductor and the sea ground conductor being close together or in the same sheath are subjected to the same temperature changes and, if the two are similar to the same variations in electrical characteristics with the result that temperature varia= tions will not im air the duplex balance providing the arti cial line is located sufliciently far out at sea that the cable beyond it is not subject to temperature changes, the temperature of the ocean bottom being substantially constant when a sufiicient depth is reached. To accomplish this advantage re quires, of course, a submerged artificial line but it has never been considered practicable to place the artificial line for a long submarine telegraph cable in a submerged container at sea in the manner required since it would not, if so placed, be available for such adjustments as might be necessary to obtain a perfect balance, or to match variations in the cable caused by repairs or changes with time. The invention provides means for obtaining an accurate balance and is destroyed even though the main artificial line be located at sea or in any other inaccessible place.

The invention will be more fully understood from a consideration of the accompanying drawing in whichFi 1 represents one embodiment thereof applied toa cable for duplex operation. Fig. 2 is a simplified circuit of aduplex bridge. I

Referring to the drawing, the terminal apparatus comprises the usual duplex equi ment including the ratio arms 7 and i joined by the apex resistance 8 to which the transmittin apparatus 10 is connected through an ad ustable contact 9. Across the corners 11 and 11 of the duplex bridge, more clearly shown in Fig. 2, is the receiving apparatus 2 which is connected to the main cable conductor 16 forming one arm of the duplex brid e and through the other arm consisting o the sea ground conductor 19 and the submerged artificial line 3, to a to ground from any point on the sea ground conductor is the same as that from an adja-' cent point on the main conductor. Consequently interfering currents induced from external sources will be neutralized as regards their efiect on the receiving instrument 2. Furthermore, temperature changes affecting the electrical characteristics of the main conductor between the points A" and B will affect the corresponding part of the sea ground conductor in the same manner and to the same degree, and consequently have no effect on the accuracy of balance.

The artificial line 3 is shown in the diagram as consisting of series resistances 5 and shunt capacities 6 connected to a common conductor 17, thence to ground connection' l which may conveniently be made pn the containing case 18 of the artificial me. a

If the main conductor and the sea ground conductor were exactly alike and if the artificial line 3 exactly balanced the cable. 16 beyond the point B, the arrangement of Fig. 2 would be sufiicient to insure proper functioning of the terminal apparatus but it'is practically impossible to insure an accurate balance between the artificial line 3 and. the cable 16' beyond the point B when the artificial line 3 is located at sea where it is inaccessible. Additional means'are therefore rovided as shown in Fig. 1 so that the circuit may be adjusted from time to time, to maintain the accuracy ofbalance required for duplex operation. This'is accom lished by connecting to the point 11 of to duplex bridge the artificial line 12 comprisinadjustable series resistances and shunt con ensers, and tothe opposite point 11 a similar artificial line 12. Artificial lines 12 and 12 may be grounded at the, common point 15.

In order that there will be no disturbance in the receiving apparatus 2 while impulses are being sent by the transmitter 10, it is necessary that ,the. potentials of points 11 and 11 be equally affected by the transmitting current.' If, however, there is a source of unbalance disturbance owing to the failure of the artificial line 3 to balance the main cable, this source of unbalance can be corrected by a change in either the artificial line 12 or the artificial line 12. As a particular case, let us suppose that the resistance 5 of artificial l1ne.3 is too large to properly balance the electrically correspondmg part of the cable 16. As a result, the transmitted signal will be reflected differently from the artificial line 3 than from the corresponding part of the cable 16, establishing a difference of otential between points 11 and 11' and pro ucing a disturbing current in the receiving apparatus 2. This disturbance may be eliminated by increasing the resistance 13 of the artificial line 14 to such a degree that a disturbance reflected therefrom will just compensate that reflected from the artificial line 3 and the balance will be thereby restored. The same result might be accomplishedby decreasing the corresponding resistance 13 in the artificial line 14.

if artificial lines 12 and 12 were of just the same impedance as the main cable, resistance 13 would have to be increased or resistance 13 diminished by just the amount I that resistance 5 is too large. However, undercertain conditions it is objectionable to have artificial lines 12 and l2 of the same impedance asthe maincable since in this case a considerable part of the incoming signals would be diverted by these artificial lines and the received signal thereby reduced. In orderto reduce the shunting effect of artificial lines 12 and 12' it may be desirable to make them of higher impedance than the main cable but in this case changes in the auxiliaryartificial lines 12 or 12' required to effect a balance would have to be larger -than the variation in the resistance 5 which it is desired to compensate. By the proper design of the artificial lines 12 and 12', the shunting effect on the rcceived signal may be reduced so as not to prove objectionable.

' As described above, the method is applied to'the ordinary cable of negligible inductance. It is understood, however, that the samemethod of correction may be applied equally Well to an inductively loaded cable :5 cable and said conductor, and means bridgsaid receiver for balancing the circuit by merely roviding artificial lines 3, 12, and 12' wit the roper amount of inductance to correspon to that of the main conductor.

What is claimed is:

1. A duplex signaling system comprising a pair of conducting signaling paths, a recelver bridged across said paths, and a separate artificial line simulating distributed ca acity vand resistance connected to each sidi;1 of the receiver in parallel with each at P 2. A duplex signaling system comprising a pair of conducting paths, one of said conducting paths' having an artificial line connected in series therein simulating distributed impedance of a portion at least of the other of said paths, a receiver bridged across said paths, and a se arate secondary artificial line simulating istributed capacity and resistance connected to each side ofthe receiver in parallel with each path.

3. A submarine cable duplex bridge system comprisinga main cable in one arm of the bridge, a return circuit comprising a section of cable core similar to that of the main cable and parallel thereto and terminating in a sea earth through an artificial line simulating'the impedance of the main cable, said section 'of cable core being directly connected to one apex of the bridge and being in an arm of the bridge difierent from said 7 main cable.

4. A duplex signaling system comprising a pairof conducting paths, a transmitter for signalling across said paths, said paths being in di erent arms of the duplex bridge, and separate artificial lines simulating distributed capacity and resistance connected to each side of the receiver in parallel with each. of said paths for balancing the circuit for duplex operation.

5. A duplex signaling system comprising a submarine cable, a conductor extending from a terminal of said cable to a deep water )oint at sea and there grounded, an artificial line at sea connected to said conductor and simulating the im edance of the cable, a receiver connected said cable and said conductor, and an auxiliary artificial line connected between one terminal of said receiver and ground and comprising sections containing series resistance and shunt capacity.

6. A duplex signaling system comprising a submarine cable, a conductor, grounded throu h an artificial line at sea, said artificial dine simulating the impedance of the cable, a receiver connected between said ing for duplex operation.

' 7. A duplex signaling system comprising T a submarine cable, a conductor ground thereover, a receiver brid ed.

tween the terminals of through an artificial line at sea, said artificial line simulating the impedance of the cable, a receiver connected between said cable and said conductor, and two secondary artificial lines connected in series and grounded at their junction bridged across said receiver.

8. A duplex signaling system comprisinga submarine cable, a conductor grounded through an artificial line at sea, said artificial line simulating the impedance of the cable, a receiver connected between said cable and said conductor and two equal adjustable artificial lines connected in series and grounded at their junction bridged across said receiver. v

9. In a duplex signaling system, a line conductor, a parallel circuit, said conductor and said parallel circuit connected to the opposite corners of a Wheatstone bridge, a receiver connectedin the diagonal thereof, two arms having adjustable condensers and adjustable resistances connected therein, and two arms having equal artificial lines.

10. A signaling system comprising a submarine cable, terminal signahng ap aratus therefor. a conductor connecting sai terminal apparatus with said cable, a second conductor similar to said first conductor extending parallel thereto from said terminal apparatus to a oint at sea, an artificial line simulating sald cable and connected to said second conductor at its sea end, a receiver in said terminal ap aratus bridging said con ductors and an a justable artificial line simulating distributed resistance and capacity connected to one side of the receiver and ground for compensating for any unbalance due to change of characteristics of the cable or sea artificial line.

11. A terminal system for a submarine cable comprising an artificial line at sea connected with the terminal of the cable through a long conductor paralleling the cable or its shore end connection, a receiver connected between said conductor and said cable, or its shore end connection, an auxiliary artificial line simulating distributed capacity and resistance associated with said conductor and said cable, or its shore end connection, said long conductor and the adjacent portion of the cable being s metrically arranged with res ect to sai receiver to prevent unbalance ue to temperature changes of the shore end of the cable adjacent said conductor.

- 12; The combination with a submarine cable of a ground therefor at sea connected with a terminal ofthe cable through along conductor paralleling the cable or its shore end connection, a receiver connected between saidconductor and said cable or its shore end connection, a main artificial line at sea connected with the sea end ofsaid conductor, and two auxiliary adjustable artificial lines IOI simulating distributed capacity and resist.

ance connected on the one hand to the ter-' minal respectively of said receiver. and on the other to ground or a terminal of said main artificial line.

13. A. duplex signaling system comprising a pair. of conducting signaling paths, each 0 which terminates in an earth connection, a receiver bridged across said pathsand a separate artificial line simulating distributed capacity and resistance connected to each side of the receiver in parallel with each path.

means 14. A duplex signalingsystem compris-' ing a p'air'of conducting paths, each of which comprises a section of submarine cable, a transmitter for'signaling thereover,

a receiver bridged across said paths and my name this 29th day of'Ap'ril AnD. 1921.

OLIVER 1a. UQKLEY; 

